Originally Posted by CrankyOne

It makes a considerable difference. First, a driver has less time to react the faster they are driving which decreases their ability to avoid incidents and leads to an increase in the overall number of incidents.

Second, vehicle speed has a huge impact on severity of injuries or fatalities. Going 40 in a 30 doubles the likelihood of a fatality while at 20 mph almost everyone will survive. Do you want to be hit by someone driving 20 mph or 30 mph?

[TABLE]
[TR]
[TD]Vehicle Speed[/TD]
[TD]Odds of Pedestrian Death, Source 1[/TD]
[TD]Odds of Pedestrian Death, Source 2[/TD]
[/TR]
[TR]
[TD]20 mph[/TD]
[TD]5%[/TD]
[TD]5%[/TD]
[/TR]
[TR]
[TD]30 mph[/TD]
[TD]45%[/TD]
[TD]37%[/TD]
[/TR]
[TR]
[TD="width: 144"]40 mph[/TD]
[TD]85%[/TD]
[TD]83%[/TD]
[/TR]
[/TABLE]

Consider too the mindset of the driver. Is someone driving 20 more likely to be more aware of their surroundings than than someone driving 40? Is someone driving 40 mph less likely to be patient of a bicycle rider and more likely to try a more dangerous pass?